1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a semiconductor device including a contact connected to the body region of a semiconductor element.
2. Description of the Background Art
Widely known semiconductor devices include a device (hereinafter referred to as “SOI device”) using an SOI substrate in which a silicon substrate, an oxide layer (BOX (buried oxide) layer), and a silicon layer (SOI (silicon on insulator) layer) are formed in this order from bottom to top. The SOI device allows reduction in parasitic capacitance, reduction in power consumption and speedup of operation, and is widely used for example in communication LSIs and portable devices.
The reduction in resistance of interconnect lines and contacts is normally an essential technique for speeding up the operation of the SOI device. In order to realize such reduction in resistance, a compound layer of silicon and metal (silicide layer) is generally formed at the connection between an element formed in the SOI device and a contact which may be the upper part of a gate wiring or source/drain region. The formation of a silicide layer is disclosed for example in Japanese Patent Application Laid-Open No. 6-204334 (1994) (FIGS. 83-84), in which a metal layer containing Ti (titanium) or Co (cobalt) is deposited by sputtering and the like on the upper part of a source/drain region defined in an SOI layer and on the upper part of a gate electrode containing polysilicon. This metal layer is then subjected to thermal processing to form a silicide layer.
As a technique for stabilizing and speeding up the operation of the SOI device, a contact is formed to be electrically connected to the body region of an element formed in the SOI device (body contact) to control the potential of the body region. Such a technique is adopted for use for example in a DTMOS (dynamic threshold voltage metal oxide semiconductor) transistor in which the gate electrode of the MOS transistor is connected through a body contact to a body region, an example of which is introduced in Japanese Patent application Laid-Open No. 2001-77368.
In the SOI device having a body contact, a leakage current is likely to flow from the body contact into a body region. Accordingly, a resistance of a certain value is desirably provided between the body contact and the body region to reduce the leakage current and power consumption. However, variations of this resistance value will disadvantageously result in variations of electrical characteristics of the SOI device.